Apolipoprotein (apo) E, a polymorphic protein with three isoforms (apoE2, apoE3, and apoE4), is essential for lipid homeostasis. Carriers of apoE4 are at higher risk for developing Alzheimer's disease (AD). The hippocampus is one of the first regions of the brain damaged in AD, and memory deficits and disorientation are among the early symptoms.
Tau protein is expressed in central nervous system and plays a critical role in the neuronal architecture by stabilizing intracellular microtubule network. Impairment of the physiological role of the tau protein either by truncation, hyperphosphorylation or by disturbing the balance between the six naturally occurring tau isoforms leads to the formation of neurofibrillary tangles (NFT), dystrophic neurites and neuropil threads. These structures represent ultrastructural hallmarks of Alzheimer's disease (AD). The major protein subunit of these structures is microtubule associated protein Tau. The amount of NFT found in autopsies of AD patients correlates with clinical symptoms including intellectual decline. Therefore, Tau protein plays a critical role in AD pathology.